Best missed 10 games in 2011 because of a serious concussion, then sat out all of last season with post-concussion problems. In many ways, Best became a living example of the NFL's evolving stance on concussions and concussion testing.

The evolution of the NFL:
Take a look at how the NFL has evolved from its humble roots, and the efforts being made to ensure it continues to grow.

"Jahvid is as fine a person and professional as I have ever worked with," Martin Mayhew, the Lions' executive vice president of football operations and general manager, said in a statement released by the team. "He was the consummate teammate and always did everything asked of him."

Best doesn't acknowledge that this is the end of his NFL career, but it's the direction things are pointing.

"My time as a member of the Lions was a very special time in my life," Best said in the team-issued statement. "My teammates, the members of the organization, the Lions fans and the people of Detroit will hold a special place in my heart. I'll always be a Lion."

If Best's career is over, he'll join Billy Simms, Bo Jackson, Greg Cook and Robert Edwards as former NFL players whose careers ended far too soon. Best totaled 1,042 yards from scrimmage, 58 catches and six touchdowns as a rookie.